I read the book Tunes For ' Toons written by Daniel Goldmark, released Oct. 2005.
The book made me very anxious what it had to say about the Fleischer's cartoons. The Fleischer 'toons attract my attentions because they use music as the basic for the story lines. In other cartoons the story might be the most important item; Fleischer starts with the tune. Goldmark gives as an example the Song Car-Tunes or Screen Songs. Two of those items I have in my collection - Down Among The Sugar Cane sung by Lillian Roth and You Try Somebody Else by Ethel Mermans. Each film is a mixture between film and cartoon and we would call it karaoke now. The starting point is the tune and the film is build around it. The vocalist sings the song and a bouncing ball jumps over the subtitles visible in the screen. In the middle of the film is always a part reserved for a cartoon.
In the early 1930s Fleischer started to use real musicians as a starting point for his Betty Boop cartoons, like Louis Armstrong, Cab Calloway or Don Redman. If you have seen these jazzy Betty Boops you know that they start with a shot of the live orchestra playing a well known tune and after a minute the cartoon continues the story line. Nowadays we knit our brows when we see Louis acting like a cannibal seamless fitting into the racial prejudice of that times. Such a performance doesn't fit into our ideas about racism and integration. The book tries to explain why the 1930s American wanted to see it that way and the book notices that critics in the 1930s in the US revolt agains these kinds of films.
When I saw the Walt Disney reissue of the Silly Symphonies on DVD, I learned that the compilers noticed before the film starts that they won't to be identified with some racial parts of the film, like a black man dressed as a cannibal or an indian with a bow and arrow.